1. Field
The present invention relates to a hydrogenation catalyst for nitro-aromatic compounds and a method for preparing the same, particularly to a hydrogenation catalyst for nitrobenzene. More particularly, the present invention relates to a hydrogenation catalyst for nitrobenzene, which is applicable for a corresponding process for preparing aromatic amino compounds by way of a reaction for hydrogenating aromatic amino compounds and demonstrates improved selectivity, reactivity and stability.
2. Description of the Related Art
Nitro-aromatic compounds, including ortho-toluidine, para-toluidine, toluene diamine prepared by processes for hydrogenating nitrobenzene, nitrotoluene and dinitrotoluene, are widely used as intermediate compounds required in various chemical processes. Especially, aniline is utilized as main raw material to prepare MDI, source material of urethane. A variety of prior arts related to the hydrogenation of nitrobenzene have been already disclosed.
In Korean Patent Notification No. 1994-6772, the method for preparing aniline by hydrogenating nitrobenzene has been mentioned, in which as an applicable catalyst, palladium or palladium-platinum catalysts deposited on a lipophilic carbon are described. In this case, metal oxides or hydroxides such as iron or nickel can be included on a main catalyst carrier. Further, as an accelerator of hydrogenation, zinc compounds can be contained in 20 to 2,000 ppm. In addition, in Korean Patent Registration No. 600546, the hydrogenation catalyst which can be utilized to hydrogenate nitro groups of nitro-aromatic compounds to corresponding amines in the presence of moisture, and the method for preparing the same have been disclosed. The main catalyst applied is described to include nickel such as nickel crystal in a size distribution of bimodal nickel crystal, and have 60 weight % to 80 weight % of nickel content (compared to total weight of catalysts) and 70% or more of recycling rate (after recycling at 100° C. for an hour). Besides, in Korean Patent Registration No. 531703, as a hydrogenation catalyst for nitro-aromatic compounds, Raney nickel catalyst which is prepared by a process comprising steps of: solidifying fused alloy that is comprised of 50 to 90 weight % of aluminum, 10 to 50 weight % of nickel, 0 to 20 weight % of iron, 0 to 15 weight % of cerium, cerium alloy metal, vanadium, niobium, tantalum, chromium, rubidium or manganese, and alternatively, additional glass forming elements, rapidly at a certain cooling speed; and treating the alloy solidified rapidly with organic or inorganic bases, has been disclosed. Furthermore, the hydrogenation catalyst supported in a powder have been disclosed in prior arts, in which active components of the hydrogenation catalyst for nitro-aromatic compounds are comprised of the first precious metal, the second precious metal and a mixture of one or more non-precious metals, wherein the first precious metal is Pt, the second precious metal is Pd, Ru or Rh, and the non-precious metal is V, Fe, Mn, Ce and/or Cr; the first precious metal is Pd, the second precious metal is Ru or Rh, and the non-precious metal is V, Fe, Mn, Ce and/or Cr; or the first precious metal is Pd, the second precious metal is Pt, and the non-precious metal is Ce and/or Cr.
In the process for hydrogenating nitro-aromatic compounds, especially nitrobenzene, a variety of adverse reactions can occur and thus by-products caused by such an adverse action, such as non-aniline compounds becomes severe anti-catalysts against the catalyst used. Moreover, conventional catalysts are found insufficient to acquire desired efficiency in respect of reaction velocity of the hydrogenation. Therefore, it is necessary to improve overall efficiency for preparing aniline, because aniline is widely used for basal raw material of urethane, dyes, medicines and the like. Further, modified catalysts also need to be newly developed.